This invention relates to a method for installation of a cured in place liner into an existing conduit by everting the liner, and more particularly to a method for preventing the portion of the liner which turns back during eversion from bonding to the inner wall of the liner as it is cured, and to the liner assembly including a turnback release protection film.
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage. The leakage may be inward from the environment into the interior or conducting portion of the pipe. Alternatively, the leakage may be outward from the conducting portion of the pipe into the surrounding environment. In either case, it is desirable to avoid this leakage.
The leakage may be due to improper installation of the original pipe, or deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive material. Cracks at or near pipe joints may be due to environmental conditions such as earthquakes or the movement of large vehicles or similar natural or man made vibrations, or other such causes. Regardless of the cause, such leakages are undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and in a possible creation of a dangerous public health hazard.
Because of ever increasing labor and machinery costs, it is increasingly more difficult and less economical to dig up and replace underground pipes or portions that may be leaking. As a result, various methods had been devised for the in place repair or rehabilitation of the existing pipelines. This avoids the expense and hazard associated with digging up and replacing the pipes or pipe sections. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform(copyright) Process and is described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, the contents of all of which are incorporated herein by reference.
In the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. The impregnated liner may be pulled into the conduit by a rope or cable and a fluid impermeable inflation bladder or tube is then everted within the liner. Generally, the liner is installed utilizing an everting process, as described in the later two identified Insituform patents.
The flexible tubular liners has a smooth layer of relatively flexible, substantially impermeable polymer coating the outside of the liner in its initial state. This impermeable layer ends up on the inside of the liner after the liner is everted during installation. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing a fluid such as water which forces the liner radially outwardly to engage and conform to the interior surface of the existing pipeline. The resin which has been impregnated to the impregnable material is then cured to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and that repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.
Generally, in the Insituform(copyright) Process, the resin impregnated liner is flat and is typically stored in layers. It is transported to a manhole adjacent to the pipeline to be lined. The leading end of the liner is sealingly clamped to the distal end of an eversion tube in order to create a fluid seal. Pressurized fluid, such as water then forces the liner to evert into the pipeline. Various means have been provided for controlling the rate in which the liner everts as it is fed into the pipeline. Typical means within the Insituform Process for controlling the feed rate of the liner is by retaining the trailing end of the resin impregnated liner as it is everted into the pipeline using a cable or hold-back rope. By restraining the trailing uneverted end of the liner, the liner does not evert too quickly, thereby ensuring that the pressure against the line is maintained throughout the everting liner.
When the liner is everted under a head of water, the liner stretches to an undeterminable length due to many different variables. This includes, but it is not limited to the inherent properties of the flexible lining material, the pressure of the everting fluid, the slope of the existing pipeline, the effects of different individuals installing the lining and the environment and condition of the existing pipeline. This requires that the installer provide a liner at least the length of the pipeline to be lined that almost always results in some portion of liner that turns-back at completion of installation.
This is the portion of the tube held by the hold-back rope remaining inside of the new cured in place lining and is identified as the xe2x80x9cturnbackxe2x80x9d portion. When turnback occurs during eversion and hot water is circulated through the everted liner to initiate the cure, the turnback portion of the lining comes into contact with the surface wall of the liner as it is being cured. In other words, during the cure cycle of the cured in place pipe installation, the impermeable polymer coating of the turnback portion comes into direct contact with the impermeable coating of the liner against the host pipe wall. The heat from the exotherm of the resin causes the impermeable layers to melt, since the temperature exceeds the melting point of the coating thereby causing the two surfaces to fuse together. After cooling the cured liner, the fused portion of the turnback portion and the lining become one.
When the cure is completed, the end of the everted resin impregnated liner extends into the downstream manhole, the remaining turnback portion of lining inside of the new cured in place liner is usually removed. The difficulty is that the remaining turnback portion of the lining tube is now fused to the lining wall. This requires a substantial amount of resources, in time and dollars to remove the remainder of the tube from inside the cured liner. This is a costly operation, especially in large diameter pipe which can be as large as 8 feet in diameter or greater. Even more critical here is that when the diameter is too small for man entry, the turnback portion now fused to the liner wall must be cut from the manhole. When access is not possible in extreme situations, the entire section of pipe must be dug up and replaced resulting in extremely prohibitive costs.
It is also difficult to resolve this problem where the turnback occurs at a bend near the end of a host pipe. Similarly, at a bend the impermeable layer comes into contact with each other and there is the possibility that the two surfaces will fuse together. Again, this can be very difficult to remove, especially if it is not possible for human entry.
Accordingly, it is highly desirable to eliminate occurrence of fusion of the thermoplastic impermeable layers of a flexible cured in place liner during the cure after eversion of the liner.
Generally speaking, in accordance with the invention, a method for eliminating the fusion of the thermoplastic impermeable surfaces of a cured in place liner during installation by eversion is provided. Fusion of the turnback portion to the lining surface is avoided by temporarily bonding a high temperature release barrier between the two facing surfaces. The film is a high melt temperature film which is applied to the trailing end of the liner by a self-tack adhesive formulated to bond to the impermeable layer and that is water insoluble. After the installed liner is cured, the end of the everted liner is removed and the remaining high temperature film removed by peeling from the upstream end of the film.
The turnback protection film is applied to the trailing end of the liner in a length equal to from about 1 to up to 5% or more of the total length of the liner. A compatible spray adhesive is applied to about one-third of the release film length at the side of the trailing end of the liner and folded over to encompass the liner completely to form a turnback liner assembly. The turnback liner assembly is then everted into the existing pipeline in the usual manner using an everting fluid. After cure of the resin, the end of the liner extending to the down stream manhole is cut and the turnback protection film remaining within the lined conduit is peeled from the lining and removed.
Accordingly, it is an object of the invention to provide an improved method for eversion of a cured in place liner in an existing conduit.
It is another object of the invention to provide an improved method for preventing turnback fusion between the thermoplastic layer of the turnback portion and the lining after eversion of a cured in place liner in an existing conduit.
It is a further object of the invention to provide an improved liner assembly having a high temperature turnback protection film releasably secured about the trailing end of the liner for preventing turnback fusion after eversion of a cured in place liner.
Still other objects and advantages of the invention will in part be obvious and in part be apparent from the specification.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the article possessing the features, properties, and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.